The present disclosure generally relates to gaskets for sealing an interface between two components.
Gaskets have long been used to seal interfaces between components in a wide variety of machines, particularly in gasoline and diesel engines. For example, head gaskets are used to create a seal between the heads of an engine and an engine block; oil pan gaskets are used to create a seal between an oil pan and an engine block; and water pump gaskets are used to create a seal around the ports of a water pump. Most gaskets are designed specifically for their particular intended use. For example, head gaskets are designed to seal against high temperatures and pressures and the generally caustic environment within the cylinders of an engine. As another example, water pump gaskets are designed to prevent the leakage of coolant, which may consist of a mixture of water and anti-freeze that is heated and under pressure.
Two performance characteristics required of most compressible gaskets are compression resistance and sealability. Compression resistance refers to the ability of a gasket to withstand high compression forces when clamped between two flange surfaces without crushing, deforming, or yielding to the point that the mechanical properties of the gasket material and ultimately the seal provided by the gasket are compromised. Sealability refers to the ability of a gasket to resist or prevent leakage of fluid both between the gasket faces and the flanges between which the gasket is clamped (referred to as “interfacial leakage”) and the ability to resist or prevent leakage of fluid through the gasket material itself (referred to as “interstitial leakage” or “bulk seal” properties).
Many different materials have been used to form gaskets. Metal gaskets traditionally have been favored because they generally have higher heat resistance, but are prone to failure in some applications due to a high level of precision needed to obtain a tight seal. In contrast, polymeric gaskets are able to conform to the surfaces more readily, but often fail over time due to chemical or physical changes in the polymer. Additionally, even prior to failure, polymeric gaskets often are perceived as failing due to oozing or creep from the sealed surfaces resulting from extrusion under pressure of the gasket. As used herein, “extrusion under pressure” refers to the radial or planar expansion or spreading of a gasket material when subject to a compression force normal to the plane of the gasket. Extrusion under pressure typically results in an undesirable permanent deformation or “compression set”.
Two characteristics of a gasket material that effect interfacial sealing performance include compression stress resistance or compression set resistance and adhesion strength. Compression set resistance of a gasket material is the ability of the material to resist failure from extrusion under pressure. Adhesion strength of a gasket material is the ability of the material to adhere to the flange surface to maintain the seal and prevent failure of the gasket.
Typical known seals that rely on adhesion force for the sealing mechanism include Room Temperature Vulcanite (RTV) that typically comprises a silicon material. RTV silicones have long been used for gasketing applications in which a liquid resin is placed between two mating parts of a fluid conduit system, the parts mated to extrude the gasketing material over the mating surfaces, and then the formulation allowed to cure. The flexibility of the resulting gasket is highly suited to the sealing requirements of mated parts, particularly parts of different materials with different coefficients of thermal expansion. Such RTV cured-after-assembly silicones have also been formulated which have good resistance of a wide variety of hostile environments.
An important part of the environment resistance which these formulations achieve is due to the strong silicone/flange surface adhesion developed by particular adhesion promoters in these formulations. However, where removability of the gasket is important, e.g. where gasket replacement may be necessary for maintenance or repair of an assembly, such strong flange surface adhesion makes the use of such cured-after-assembly gaskets undesirable. Moreover, cured-after-assembly gaskets may create problems when an excessive amount of RTV is used because uncured fillets may be extruded into fluid passageways where they may contaminate fluids or cure so as to partially or completely block a passageway.
In contrast to RTV or liquid, cured-after-assembly gaskets, it is also known to utilize preformed compression gaskets as seals between automotive engine parts. Compression gaskets are easily removed and replaced but suffer the disadvantage that an inventory of gaskets must be maintained for each configuration of mating parts. Further, “compression set” can limit the performance of gasket materials under certain operating conditions.
Thus, there is a need for an improved gasket with improved performance characteristics and sealing properties.